Wellbore operations employ pipe strings, sometimes called drill, production or work strings, each used for drilling and/or servicing. The pipe string can comprise a bottom hole assembly such as, when drilling, a drill bit attached to sections of drill pipe. As the well is drilled or serviced, additional sections of drill pipe are added to the pipe string to extend its length until the bottom hole assembly is deep enough to reach a depth of interest. Sections of pipe are joined together using threaded connections on the pipe, often referred to as “pin” and “box” connections, where the pin of one section of pipe is threaded into the box of an adjoining section of pipe. When the pipe string is removed from the wellbore, the sections of pipe can be removed from the pipe string by unthreading the connections and setting aside a pipe section. Generally, one section of pipe is secured protruding from the rig floor. This section is often referred to as the stump. The stump may have an open inner diameter that is in communication with the bottom hole assembly in the depths of the well.
Sometimes during operations, it is necessary to plug the inner diameter of the stump. For example, a plug may be installed to stop fluids from passing up through the string and from being released at the stump. As another example, a plug may be installed if there is a stoppage in the drilling or servicing operation.
The plug used for installation in the stump is called a safety valve or a stabbing valve. The safety valve has a threaded connection that threads into the stump's exposed threaded connection and an integral valve that can be opened or closed to open the inner diameter of the pipe string at the stump. The safety valve must be kept at the ready. Typically, the safety valve is set on the rig work floor and must be manually lifted into place or the safety valve is suspended from a tugger winch and must be hoisted into position if needed.
With the introduction of slant rigs, difficulties have arisen in the use of safety valves.